1. Field of the Invention
The disclosure relates to drilling fluid circulation systems. More particularly, the disclosure relates to top drive adapters that enable dual flow through a top drive portion of a drilling fluid circulation system.
2. Description of Related Art
A drilling fluid circulation system is defined by the complete circuitous path and the equipment through which the drilling fluid travels while drilling operations are ongoing. In conventional drilling practices, the drilling fluid circulation system starts at the mud tanks containing drilling fluid (also known as mud or drilling mud). Pumps are used to transfer the drilling fluid through various equipment and piping to a mud hose. From the mud hose, the drilling fluid is pumped down the bore of a drill string, which is suspended in a borehole. The drilling fluid flows into the bottom of the borehole through the drill bit at the bottom of the drill string. At the bottom of the borehole, the drilling fluid commingles with earth cuttings made by the drill bit. The drilling fluid with the earth cuttings (and other materials that the drilling fluid picks up in the borehole) is forced up a return annulus defined by the space between the drill string and the borehole wall to a mud treatment system, which removes the cuttings and extraneous materials from the drilling fluid and returns the clean drilling fluid to the mud tanks. The drilling fluid circulation system operates continuously during the drilling operation.
In conventional drilling with a top drive, the top drive is coupled to the top of the drill string and used to rotate the drill string. The top drive has a conduit through which drilling fluid can flow from the mud hose into the drill string. The mud hose is coupled to the top drive by a swivel, which is a type of sealing rotary joint. A valve is arranged between the conduit in the top drive and the drill pipe of the drill string. The valve is known by many names in the field, e.g., safety valve, kelly valve, internal blowout preventer, and kelly cock. The valve may perform one or more functions. A first function is that of preventing drilling fluid in the conduit from being dumped on the rig floor when the drill string is disconnected from the top drive, as may be the case when a pipe joint is to be attached to or removed from the drill string. Another function is to prevent drilling fluid in the drill string from flowing back through the conduit in the top drive to the mud hose. In conventional drilling with a top drive, the swivel and valve provide a single flow path for fluid exchange between the mud hose and the drill pipe.
Recently, a new drilling method has been proposed that involves use of a drill string having a dual-flow drill pipe, i.e., a drill pipe having two concentric fluid conduits. In the proposed drilling method, drilling fluid is pumped down the outer conduit of the dual-flow drill pipe. The drilling fluid in the outer conduit flows out the face of the drill bit and into the bottom of the borehole. At the bottom of the borehole, the drilling fluid commingles with earth cuttings made by the drill bit. So far, this operates the same way as the conventional drilling method. However, the proposed new drilling method includes directing the drilling fluid with earth cuttings back into the drill string, and particularly into the inner conduit of the dual-flow drill pipe, through openings in the wall of the drill string. The drilling fluid flows up the inner conduit of the dual-flow drill pipe to the mud treatment system at the surface. Thus, in the new drilling method, the return annulus is located inside the drill string instead of between the drill string and the borehole wall.
There is a need for top drive adapters, e.g., valve and swivel, that would enable the new drilling method with a top drive.